1. Field of the Invention
This invention relates to a steering gear and steering system for operating the roadwheels of a vehicle, particularly the rear wheels of a vehicle normally employing front wheel steering.
2. Disclosure Information
Multiple axle steering systems typically in use in automotive vehicles employ a main steering gear for providing gross steering inputs at either the front or rear of the vehicle. A secondary steering gear for providing minor steering inputs to the roadwheels of the opposing axle is the subject of the present invention. It has been determined that undesirable handling characteristics will result if the auxiliary steering system is capable of being backdriven. As used herein, the term "backdriven" means that the steered roadwheel may be rotated about its kingpin axis in response to side forces caused by steering maneuvers, road roughness, braking, acceleration, or other types of inputs into the roadwheels. As used herein, the term "nonreversible" means a steering gear and system which cannot be backdriven. This backdrive phenomenon is objectionable insofar as it detracts from the ability to control the steering angle of the affected roadwheel. In shaft-type four-wheel steer systems such as that exemplified by U.S. Pat. No. 4,582,334, in which a rotatable shaft couples the front and rear steering gears of the vehicle, the backdrive phenomenon may cause the steering wheel to oscillate in the driver's hands. In other known four wheel steering systems, springs are used for centering the rear steering gear so as to resist reversibility. This will increase the amount of power required for operating the steering gear. In other types of electronically controlled systems such as that illustrated in U.S. Pat. No. 4,695,069, the backdrive phenomenon may cause the motor powering the system to rotate in response to the backdrive force when no rotation was called for by the system control module. A further problem noted with the system of the '069 patent resides in the fact that the rear steering gear is resiliently coupled to the roadwheel. This resilient coupling will allow compliance steering of the roadwheel which will undermine the ability of the steering system to control the steered attitude of the wheel.
It is an object of the present invention to provide a steering gear and steering system suitable for use as an auxiliary steering system--e.g. at the rear of a normally front-steered vehicle, which will provide precise control of the steered roadwheels.
It is yet another object of the present invention to provide a rear wheel steering system which cannot be backdriven.
Other objects, features and advantages of the present invention will become apparent to the reader of this specification.